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Method and system for pulp processing using cold caustic extraction with alkaline filtrate reuse

a technology of cold caustic extraction and alkali filtrate, which is applied in the field of pulp processing, can solve the problems of increasing production costs and preventing high quality pulp from being achieved, and achieve the effects of enhancing the purity of brown stock and resulting purified pulp, and increasing efficiency

Active Publication Date: 2011-11-10
BAHIA SPECIALTY CELLULOSE
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0019]According to one or more embodiments, a method and system for pulp manufacturing using cold caustic extraction in conjunction with a kraft process includes the steps of delignifying organic pulp-containing materials in a digester, treating a resulting brown stock to yield semi-purified pulp, extracting the semi-purified pulp with a caustic solution to yield a purified pulp and a solution containing hemicellulose, separating the hemicellulose-containing solution from the purified pulp, washing the purified pulp and collecting an alkaline filtrate resulting therefrom, concentrating the alkaline filtrate, and utilizing at least a portion of the concentrated alkaline filtrate in the digester. The concentrated alkaline filtrate may gradually replace a different cooking liquor that is initially used to start up the cooking process, thereby resulting in increased efficiency.
[0020]In certain embodiments, an alkaline filtrate is concentrated to form a solution containing, for example, 90 grams or more per liter of effective alkali as sodium hydroxide. By utilizing the concentrated alkaline filtrate as part of the cooking liquor, the purity of the brown stock and resulting purified pulp may be enhanced.

Problems solved by technology

This can prevent high quality pulp from being achieved.
The recovery process and the provision of a new alkali source tends to result in increased production costs.

Method used

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  • Method and system for pulp processing using cold caustic extraction with alkaline filtrate reuse
  • Method and system for pulp processing using cold caustic extraction with alkaline filtrate reuse
  • Method and system for pulp processing using cold caustic extraction with alkaline filtrate reuse

Examples

Experimental program
Comparison scheme
Effect test

example 1

Concentration of CCE Filtrate

[0066]According to a first example, a stream of very diluted caustic solution at an effective alkali concentration of 5.6 grams NaOH per liter is introduced into the fifth effect 327 as shown in FIG. 3 to start the plant running and to observe its behavior with different alkali concentration levels. Water is removed from the solution at a reduced pressure of −0.73 bar at a temperature between 51.5° C. and 56.8° C. After 4 hours and 30 minutes, a caustic solution with an effective alkali concentration of about 50 gram NaOH per liter, similar to the raw CCE filtrate, is fed in the fifth effect getting at the outlet of the sixth effect from an inlet filtrate concentration about 50 grams NaOH per liter. Table I lists the flow rate, temperature, effective alkali concentration and vacuum level as a function of time.

TABLE IEffective alkaliFeeding(g NaOH / l)TimeFlowTemperatureInput atOutput atPressure(min.)(m3 / h)(° C.)Effect 5Effect 6(bar)035051.55.6−0.736537054....

example 2

Conventional Kraft Process

[0067]According to a second example, an experimental kraft process is carried out in a bench scale digester (approximately 20 liters volume) to simulate the industrial processing. A 20-liter bench scale digester is pre-heated with steam to 120° C. over a period of 30 minutes. A suitable quantity (such as 4.7 kg oven dry basis) of eucalyptus wood chip is added to the digester. The digester is heated to 165° C. over a period of 60 minutes and held at 165° C. for a further 40 minutes to complete the pre-hydrolysis stage. For a conventional kraft process (not using filtrates from the CCE), 4.51 liters of a first white liquor (“WL1”) with an effective alkali concentration of 124.7 g NaOH per liter is added to the digester over fifteen minutes at a temperature of 152° C. The typical alkali charge for the neutralization is about 12% of Effective Alkali (EA) as NaOH on the dry chips weight. The digester is then filled with 10.8 liters of hot black liquor with an ef...

example 3

Use of Weak Concentration CCE Filtrate as Neutralization Solution and Cooking Solution

[0068]According to a third example, the same pulping process as described in Example 2 is repeated, except that the white liquor for the neutralization and cooking stages is replaced with a filtrate from the CCE step having an EA of 54 g NaOH per liter (“CCE54”). The Neutralysate has a pH of 11.0, and the cooking mixture has an EoC of 18.5 g NaOH per liter. The P factor for the pre-hydrolysis is 297 and the H factor for the cooking reaction is 419. For this example the total equivalent effective alkali charge on the wood are respectively: 12% EA as NaOH for the Neutralization phase and 11% EA as NaOH for the Cooking phase.

[0069]The resulting brown stock shows a Kappa Number of 10.8, a viscosity of 1118 ml / g, an S10 solubility of 4.5% and an S18 solubility of 3.6%. The reaction has a 40.4% yield. When screened, the mixture has a 0.09% rejection rate, resulting in a screening yield of 40.3%.

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Abstract

A method for pulp processing includes a cold caustic extraction stage in which the spent cold caustic solution and the spent liquid used to wash the extracted pulp are concentrated by an evaporation system. The concentrated liquid can be used as part of the neutralization and cooking liquor in the pulp process, leading to increased efficiency without significant reduction in pulp quality. Highly concentrated filtrate from the cold caustic extraction stage may help reduce hemicellulose deposition on wood fiber during the cooking step.

Description

BACKGROUND OF THE INVENTION[0001]1) Field of the Invention[0002]The field of the invention generally relates to pulp processing and, more specifically, to an improved method and system for treating effluents from cold caustic extraction in connection with a kraft chemical pulping process.[0003]2) Background[0004]Pulp from wood and plant materials has a large number of commercial uses. Although one of the most common uses is in paper manufacturing, pulp can also be used to produce a number of other products including rayon and other synthetic materials, as well as cellulose acetate and cellulose esters, which are used, for example, in the manufacture of filter tow, cloth, packaging films, and explosives.[0005]A number of chemical and mechanical methods exist for processing wood and plant materials in order to manufacture pulp and paper. The basic processing steps include preparing the raw material (e.g., debarking and chipping), separating the wood fibers by mechanical or chemical me...

Claims

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Application Information

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IPC IPC(8): D21C9/02
CPCD21C3/02D21C11/0007D21C11/0042D21C11/04D21H17/66D21C1/04D21C9/004D21D5/00D21C1/02
Inventor LEITE, MARCELO MOREIRA
Owner BAHIA SPECIALTY CELLULOSE
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